The Affordable Care Act is constitutional in
part and unconstitutional in part. The individual mandate cannot be upheld as
an exercise of Congress’s power under the Commerce Clause. That Clause
authorizes Congress to regulate interstate commerce, not to order individuals
to engage in it. In this case, however, it is reasonable to construe what
Congress has done as increasing taxes on those who have a certain amount of
income, but choose to go without health insurance. Such legislation is within
Congress’s power to tax.

As for the Medicaid expansion, that portion of
the Affordable Care Act violates the Constitution by threatening existing
Medicaid funding. Congress has no authority to order the States to regulate
according to its instructions. Congress may offer the States grants and require
the States to comply with accompanying conditions, but the States must have a
genuine choice whether to accept the offer.[45]

[ . . . ]

The Federal Government does not have the power
to order people to buy health insurance. Section 5000A [of the Internal
Revenue Code] would therefore be unconstitutional if read as a command. The
Federal Government does have the power to impose a tax on those
without health insurance. Section 5000A is therefore constitutional, because it
can reasonably be read as a tax.[46]

Justices Scalia, Kennedy,
Thomas, and Alito signed a joint dissent in which they argued that the
individual mandate was unconstitutional because it represented an attempt by
Congress to regulate beyond its power under the Commerce Clause.[49] Further, they argued that
reclassifying the Individual Mandate as a tax rather than a penalty in order to
sustain its constitutionality was not to interpret the statute but to re-write
it, which they deemed a troubling exercise of judicial power.[50]

There was speculation that
the joint dissent was the original internal majority opinion, and that Chief
Justice Roberts' vote changed some time between March and the public issuance
of the decision.[51][52][53] Paul Campos, a professor of law at
the University of Colorado at Boulder, for example, quotes the following
passage from the joint dissent:[51]

Finally, we
must observe that rewriting §5000A as a tax in order to sustain its
constitutionality would force us to confront a difficult constitutional
question: whether this is a direct tax that must be apportioned among the
States according to their population. Art. I, §9, cl. 4. Perhaps it is not (we
have no need to address the point); but the meaning of the Direct Tax Clause is
famously unclear, and its application here is a question of first impression
that deserves more thoughtful consideration.

Campos then concludes that: "The dissenters are saying that construing
the mandate as a tax would require them to address a constitutional question
that they don’t have to address. But the only reason the Court would not have
to address this question is if the majority in fact refused to construe the
mandate as a tax – which is exactly what the Court’s majority ended up doing.